1. Field of the Invention
The present invention relates to a radiation sensitive refractive index changing composition, a refractive index pattern forming method, a refractive index pattern and an optical material. More specifically, it relates to a novel radiation sensitive refractive index changing composition which is used in the optoelectronic and display fields, a refractive index pattern forming method, a refractive index pattern and an optical material.
2. Prior Art
In the current society called xe2x80x9cmulti-media societyxe2x80x9d, refractive index distribution type optically molded products each consisting of different refractive index regions are in great demand. The products include not only optical fibers for transmitting information but also optical diffraction gratings having a periodical change in refractive index, optical memories to which information is written at sites having different refractive indices, optically coupled elements such as optical IC""s having a fine refractive index pattern, optical control elements, optical modulation elements and optical transmission elements.
The refractive index distribution type optically molded products are divided into two types: one having a continuous refractive index distribution, such as GI type optical fibers (to be referred to as xe2x80x9cGRIN optically molded productsxe2x80x9d hereinafter) and the other having a discontinuous refractive index distribution, such as optical diffraction gratings and SI type optical waveguides.
The GRIN optically molded products are attracting much attention as the next-generation optically molded products. For example, a GI type optical fiber whose refractive index is reduced from the center axis of the core of the optical fiber to the periphery in a parabolic form enables the transmission of a great volume of information. A GRIN lens whose refractive index continuously changes therein is used as a reading lens for use in copiers, spherical lens for connecting fibers, or micro-lens, making use of its characteristic features that it has refractive power even with a flat surface and that it is free from spherical aberration.
A large number of methods of producing the above GRIN optically molded products have been proposed up till now. For example, JP-A 9-133813, JP-A 8-336911, JP-A 8-337609, JP-A 3-192310, JP-A 5-60931 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d), WO93/19505 and WO94/04949 disclose a method of obtaining a GI type optical fiber by dispersing low molecular weight compounds or a monomer into a polymer and continuously distributing its concentration. JP-A 62-25705 discloses that a GI type rod-like optically molded product or optical fiber is obtained by photo-copolymerizing two or more vinyl monomers having different diffraction indices and reactivity rations. Further, JP-A 7-56026 discloses a method of obtaining a refractive index distribution by forming a polymer A having a photo-reactive functional group, dispersing a compound B having a lower refractive index than the polymer A into the polymer A to form the concentration distribution of the compound B and photo-reacting the polymer A with the compound B.
Some methods of producing GRIN optically molded products of an inorganic material have also been proposed. One of them is, for example, a method of producing a GI type rod by adding high-refractive index thallium to rod-like glass essentially composed of silicon or lead, immersing the glass in a molten solution containing low-refractive index potassium, and forming a potassium concentration distribution by ion exchange.
A GRIN lens can be obtained likewise by applying the above method to a short rod, that is, lens-like optically molded product. Alternatively, the GI type rod produced by the above method may be sliced.
As one of methods of producing an optically molded product having a fine refractive index pattern, such as the above optical diffraction grating or optical IC, there is known a technology for obtaining a change in refractive index by causing a photochemical reaction in a molded product by the irradiation of light. For instance, in the case of an inorganic material, glass doped with germanium is irradiated with light to change its refractive index to produce an optical diffraction grating. In the case of an organic material, the above technology is known as a photochromic reaction or photo bleaching and JP-A 7-92313 discloses a technology for obtaining an optical diffraction grating by causing a change in refractive index by irradiating a material containing low molecular weight compounds having photochemical reactivity dispersed in a polymer with a laser beam. Further, JP-A 9-178901 has recently proposed that this technology is applied to the production of a GRIN optically molded product. This method provides a continuous refractive index distribution in a depth direction with respect to irradiation, making use of the fact that light irradiated onto a molded product is absorbed and weakened in intensity.
However, in the refractive index distributions obtained with the above conventional materials, the maximum refractive index difference is about 0.001 to 0.02 and it is difficult to provide a wider refractive index distribution in order to prevent an optical loss and suppress the malfunction of a circuit.
When the above conventional materials are used under the condition that light having a wavelength close to the wavelength used for changing the refractive index passes therethrough after a refractive index distribution is formed, it is impossible to prevent such a phenomenon that a gradual change in refractive index occurs, thereby deteriorating the materials.
The present invention has been made in view of the above problems of the prior art.
That is, it is an object of the present invention to provide a radiation sensitive refractive index changing composition whose refractive index of materials is changed by a simple method, whose changed refractive index difference is sufficiently large, and which can provide a stable refractive index pattern and a stable optical material regardless of use conditions.
It is another object of the present invention to provide a radiation sensitive refractive index changing composition which forms fine pores upon exposure to radiation, retains the formed fine pores stably, and provides a refractive index pattern having high film strength although it has a large number of fine pores.
It is still another object of the present invention to provide a method of forming a refractive index pattern from the above composition of the present invention.
It is a further object of the present invention to provide a refractive index pattern or an optical material produced by the above method of the present invention.
Other objects and advantages of the present invention will become apparent from the following description.
Means for Solving the Problem
According to the present invention, firstly, the above objects and advantages of the present invention are attained by a radiation sensitive refractive index changing composition comprising (A) a decomposable compound, (B) anon-decomposable compound having a lower refractive index than the decomposable compound (A), (C) a radiation sensitive decomposer and (D) a stabilizer.
Secondly, the above objects and advantages of the present invention are attained by a refractive index pattern forming method comprising exposing a radiation sensitive refractive index changing composition comprising (A) a decomposable compound, (B) a non-decomposable compound having a lower refractive index than the decomposable compound (A), (C) a radiation sensitive decomposer and (D) a stabilizer to radiation and heating to react the stabilizer (D) with the decomposable compound (A) of an unexposed portion.
Thirdly, the above objects and advantages of the present invention are attained by a refractive index pattern forming method comprising exposing a refractive index changing composition comprising (A) a decomposable compound, (B) a non-decomposable compound having a lower refractive index than the decomposable compound (A) and (C) a radiation sensitive decomposer to radiation through a pattern mask and treating the composition with (D) a stabilizer to react the decomposable compound (A) of an unexposed portion with the stabilizer (D).
In the fourth place, the above objects and advantages of the present invention are attained by a refractive index pattern forming method comprising exposing a refractive index changing composition comprising (A) a decomposable compound, (B) a non-decomposable compound having a lower refractive index than the decomposable compound (A) and (C) a radiation sensitive decomposer to radiation through a pattern mask and heating to decompose the decomposable polymer of an unexposed portion.
In the fifth place, the above objects and advantages of the present invention are attained by a refractive index pattern formed by any one of the above refractive index pattern forming methods.
In the sixth place, the above objects and advantages of the present invention are attained by an optical material formed by any one of the above refractive index pattern forming methods.